Multiply.
Answer: $8{,}135 \times48$ and $81.35\times48$ multiply the same digits in the same order. So, the product of both problems will also have the same digits in the same order. Let's multiply $8{,}135\times 48$. Then we can estimate to place the decimal point in the product of $81.35 \times 48$. $\begin{aligned} 8{,}135&\\ \underline{ \times 48}&\\ 40}\\ 240}\\ 800}\\ 64{,}000}\\ 200}\\ 1{,}200}\\ 4{,}000}\\ \underline{+320{,}000}}\\ 390{,}480 \end{aligned}$ Let's estimate to place the decimal in $81.35 \times48$. $\begin{aligned} 81.35 \times 48 &\approx 80\times 50\\\\ &\approx4{,}000 \end{aligned}$ Where can we place the decimal in $390{,}480$ to get a product close to $4{,}000$ ? $3{,}904.80=81.35 \times48$